Set two stylesheets in position. Edit the file paths in the script accordingly. Save the script in ~/.config/dwb/userscripts/ and make it executable. Restart the browser. If everything went right, then xg keys will be switching between your two stylesheets.

The problem you will notice is that there’s no way back to the author-set stylesheets after you switched to user stylesheets. This is precisely where duplicate tab comes in handy. Duplicate tab will open up the same address in a new tab and reload author stylesheets.